In order to print high quality images on a recording medium it is important to know what kind of media is about to be printed. In the case of inkjet, for example, preferred recording conditions differ for different type of media, partly because different media interact differently with ink. For example, ink is able to wick along the paper fibers in plain paper, so that the spot of ink on the paper is enlarged and irregularly shaped relative to the drop of ink that strikes the paper. Media, which are specially formulated for high quality images, such as photographs, typically have an ink-receiving layer that absorbs the ink in a more controllable fashion, so that the spot size and shape are more regular. Because the colorants are trapped closer to the paper surface, and because a larger quantity of ink can be printed, (the associated carrier fluids being absorbed), an image printed on photographic print media has more vibrant colors than the same image printed on plain paper.
The appropriate amount of ink to use for printing an image on one type of media is different than printing on another type of media. If plain paper receives the same quantity of ink, more appropriately deposited in order to print a high-density image such as a photo that would be used for that same image on photographic print media, the plain paper may not be able to dry quickly enough. Even worse, the plain paper may cockle or buckle in the presence of excess ink, so that the printhead crashes into the printed image, thus smearing the image, but also possibly damaging the printhead. Even for two different types or grades of photographic print media, the amount of ink or number of passes to lay down an image for good tradeoffs in printing quality and printing throughput will be different. It is, therefore, important when receiving image-related data on a specific image to be printed, that the specific image be rendered appropriately for a specific media type that the image will be printed on. Image rendering is defined herein as determining data corresponding to: a) the appropriate amount of ink to deposit at particular pixel locations of the image; b) the number of multiple passes needed to lay the ink down on the media in light of ink-to-ink and ink-to-media interactions; and c) the type of pattern needed to produce the image. Image rendering is related to an entire printing job; for example, if a print job consists of five pages, typically all five pages would be rendered before printing the first page of the print job. The images printed on the different pages may be different images (e.g. successive pages of a document) or they may be the same image printed on another page (e.g. multiple copies of an image).
Various means are known in the art for providing information to the printer or to an associated host computer regarding the type of media (e.g. glossy media or matte media of various grades, or plain paper) that is in the input tray of the printer. For example, the user may enter information on media type. Alternatively, there may be a barcode printed on the backside of the media that is read to provide information on media type as a sheet of media is picked from the input tray and fed toward the printing mechanism. Alternatively, media characteristics such as optical reflectance can be used to distinguish among media types. Generally, the processes for automatic media type detection require several seconds (e.g. 5 to 6 seconds) to provide accurate media-related information on media type. For competitive printers today, it is important to achieve excellent print quality at fast printing throughput. In particular, a user may be dissatisfied if the time required to print the first page of a print job is excessive.
In addition to the time required for media detection, there is also additional time required for rendering of the image for printing. In conventional printers, the media type is detected first and then the image rendering is done specifically for that media type. This is a workable method, but it introduces additional time to print the first print of a print job, because the media type detection is done prior to the start of image rendering for the print job.
U.S. Pat. No. 6,830,398 discloses one method providing faster printing throughput while enabling automatic media type detection prior to controlling conditions in the printing operation. In '398 a load detector is provided for detecting that recording media has been loaded into the printer. In addition, there is provided a sensor, such as a reflective optical sensor, that can discriminate the type of media type after the media has been loaded in the input but before paper feeding starts. In '398, when the printer is turned on, or after media loading has been detected, the sensor obtains information about the media type, even before the first page of media is picked for feeding to print a print job. However, conventional printers do not have a sensor capable of reliably discriminating paper type as described in '398. For example, the sensor in '398 would have difficulty discriminating between matte paper versus plain paper. To date, it has been found that improved reliability of media type detection is provided when the sensor (such as an optical reflective sensor) and the media are moved relative to one another during the sensing operation. Thus, an improved method of printing is needed that provides reliable, automatic detection of media type, and fast throughput printing of images that are rendered appropriately, while using available sensors for media type detection.